Derivatives

viviparity

Oviparity with free-swimming larvae is the most common, but direct terrestrial development and viviparity (with attendant internal fertilization) are known in toads as well.

The evolution of viviparity, which frees the mother from having to deposit eggs on land, and the tailfirst birth of the young imply that Carsosaurus was well on its way to a more fully aquatic lifestyle.

Direct development and viviparity have evolved in all three groups of Lissamphibia: frogs, salamanders and caecilians.

Origin

Some vipers give birth to live young which have hatched from eggs within the parent's body, whereas the eggs of most snakes are laid before they hatch. The name viper derives from the fact they are viviparous (‘producing live young’ M17th), coming from Latin vivus ‘alive’, as in vivisection (early 18th century), and parere ‘to bring forth’, the source of parent (Late Middle English). The phrase a viper in your bosom, ‘a person you have helped but who has behaved treacherously towards you’, comes from one of Aesop's fables in which a viper reared close to a person's chest eventually bites its nurturer. See also adder, snake